Hmmm, interesting. I've got the OEM sides/rears in parallel (1 ohm) running off one channel pair on the HD900/5. The fronts (4 ohm) are driven by the HD600/4. With gains set to minimum on "low" (2V) the rears are a few dB louder than the front doors. Theoretically, the max output of the HD900/5 at 1 ohm is 75W and that of the HD600/4 at 4 ohm 150W, so the fronts should be a lot louder, but they are not. I'm not worried about it though since I can raise the gains on the front channels to compensate.

The "low/High" input switch discussion though has got me thinking. I've had a problem with noise on the HD900/5 amp. When I switch from low to high, the noise goes away but of course the output level gets reduced and of I raise the gain to compensate, the noise comes right back. I was thinking, since the MS-8's speaker level outputs are of very good quality, what if I used those instead of the low level RCAs? Any potential downsides to doing that? This may be a good solution since it would kill 2 birds with one stone - getting rid of the engine noise AND utilizing the reportedly superior input option on the HD amps.

Hmmm, interesting. I've got the OEM sides/rears in parallel (1 ohm) running off one channel pair on the HD900/5. The fronts (4 ohm) are driven by the HD600/4. With gains set to minimum on "low" (2V) the rears are a few dB louder than the front doors. Theoretically, the max output of the HD900/5 at 1 ohm is 75W and that of the HD600/4 at 4 ohm 150W, so the fronts should be a lot louder, but they are not. I'm not worried about it though since I can raise the gains on the front channels to compensate.

The "low/High" input switch discussion though has got me thinking. I've had a problem with noise on the HD900/5 amp. When I switch from low to high, the noise goes away but of course the output level gets reduced and of I raise the gain to compensate, the noise comes right back. I was thinking, since the MS-8's speaker level outputs are of very good quality, what if I used those instead of the low level RCAs? Any potential downsides to doing that? This may be a good solution since it would kill 2 birds with one stone - getting rid of the engine noise AND utilizing the reportedly superior input option on the HD amps.

I do not see a problem with that as the speaker outputs of the MS-8 are about 60W at 2ohms already. And because the rear speakers are there just for surround effects (Logic7 processing on) and high passed then there's no real need of higher power going there.

It is my understanding that the input voltage rating on the amp input is in RMS, not max volts. At 18W RMS at 4 ohm it would seem the MS-8 is capable of outputting a maximum of 8.5V RMS. Close enough for me, especially since I am not thinking about subwoofer outputs, rather midrange outputs.

It is my understanding that the input voltage rating on the amp input is in RMS, not max volts. At 18W RMS at 4 ohm it would seem the MS-8 is capable of outputting a maximum of 8.5V RMS. Close enough for me, especially since I am not thinking about subwoofer outputs, rather midrange outputs.

Just try it then... RMS is not peak, peak power is about double the RMS. Most probably it will work fine as the HD 8V is actually in RMS, which equates to about 11.5V peak.

The only difference that I know of is that the HD900/5 was a Marine version, the HD600/4 (one brand new and the other used) were not.

I asked the customer to swap 600/4 to see if anything changes.

It sounds to me quite decent, until attention is paid to the imbalance in sound level between the front and rears (fronts are the EPS 4ohms, rears are the rear/sides in parallel =2ohms). I have not found such an imbalance with any of my 2 PDX installs with the exact same OEM EPS speakers in the same exact configuration.

Technic,

The one HD-600/4 I came over with was NIB from JL. I did switch the amps (HD-600/4s) and I got the same uneven power output with the 2ohms vs 4ohms!

Hmmm, interesting. I've got the OEM sides/rears in parallel (1 ohm) running off one channel pair on the HD900/5. The fronts (4 ohm) are driven by the HD600/4. With gains set to minimum on "low" (2V) the rears are a few dB louder than the front doors. Theoretically, the max output of the HD900/5 at 1 ohm is 75W and that of the HD600/4 at 4 ohm 150W, so the fronts should be a lot louder, but they are not. I'm not worried about it though since I can raise the gains on the front channels to compensate.

The "low/High" input switch discussion though has got me thinking. I've had a problem with noise on the HD900/5 amp. When I switch from low to high, the noise goes away but of course the output level gets reduced and of I raise the gain to compensate, the noise comes right back. I was thinking, since the MS-8's speaker level outputs are of very good quality, what if I used those instead of the low level RCAs? Any potential downsides to doing that? This may be a good solution since it would kill 2 birds with one stone - getting rid of the engine noise AND utilizing the reportedly superior input option on the HD amps.

kaigoss69,

I also have "engine noise" with the HD-600/4 but only when I use unbalanced outputs from the MS-8.

Hmmm, interesting. I've got the OEM sides/rears in parallel (1 ohm) running off one channel pair on the HD900/5. The fronts (4 ohm) are driven by the HD600/4. With gains set to minimum on &quot;low&quot; (2V) the rears are a few dB louder than the front doors. Theoretically, the max output of the HD900/5 at 1 ohm is 75W and that of the HD600/4 at 4 ohm 150W, so the fronts should be a lot louder, but they are not. I'm not worried about it though since I can raise the gains on the front channels to compensate.

The &quot;low/High&quot; input switch discussion though has got me thinking. I've had a problem with noise on the HD900/5 amp. When I switch from low to high, the noise goes away but of course the output level gets reduced and of I raise the gain to compensate, the noise comes right back. I was thinking, since the MS-8's speaker level outputs are of very good quality, what if I used those instead of the low level RCAs? Any potential downsides to doing that? This may be a good solution since it would kill 2 birds with one stone - getting rid of the engine noise AND utilizing the reportedly superior input option on the HD amps.

kaigoss69,

I also have &quot;engine noise&quot; with the HD-600/4 but only when I use unbalanced outputs from the MS-8.

So are you now using the high level outputs? I have a HD600 and a HD900. The HD600 is dead silent. The noise on the HD900 reduces slightly when I unplug all RCAs but does not go away. They are both grounded at the same location. So one of your Amos had noise and the others didn't just like in my case?

So are you now using the high level outputs? I have a HD600 and a HD900. The HD600 is dead silent. The noise on the HD900 reduces slightly when I unplug all RCAs but does not go away. They are both grounded at the same location. So one of your Amos had noise and the others didn't just like in my case?

I think it has to be. The 900/5 has a bit of a reputation for underperforming relative to expectation... Not that it doesn't meet spec, I don't know, but it may not exceed spec by as much. To jam 900 watts and 5 channels into the same form factor, SOMETHING had to give...

I think it has to be. The 900/5 has a bit of a reputation for underperforming relative to expectation... Not that it doesn't meet spec, I don't know, but it may not exceed spec by as much. To jam 900 watts and 5 channels into the same form factor, SOMETHING had to give...

Thanks for that input. In my case I think the compromise works well for the bridged center and more efficient rears. 1) would you agree 2) based on your experience do you think ill see this noise kaigoss has?

The jury is still out on the HD amps... two years ago I installed a HD900/5 in a HiFi M3 and it was great. Very straight forward install, sounded great without any processor.

Fast forward two years and a coded EPS-HiFi M3 with two HD600/4 (the one in the picture) and no processing showed some changes in sound quality and compatibility that I'm still trying to understand. For example, although the power output should be the same all the way down to 1.5ohms, a 2 ohms load sounds considerably louder than a 4ohms load. Setting their input level to high sounds slightly better than setting it at low, as it should be (it is HiFi as it was with the HD900/5). Installing a MS-8 in between the CIC and the HD amps have shown similar results, so it is not a matter of balanced inputs.

No XD amp have shown issues like that with HiFi outputs.

Something must have changed in these amps that when the customer contacted JL Audio to ask about these issues their "fix" was to install a Cleansweep.

Quote:

Originally Posted by Technic

According to the customer, yes. I did not install the MS-8, I only calibrated it once after the install and still it sounded to me that the rears were getting a slightly higher power than the fronts.

Quote:

Originally Posted by Technic

I tried both and still I could hear higher volume in the back. To be clear, this is not higher as in "damn this is louder!" than the fronts, just enough to notice. And because I already noticed this without the MS-8 then it became obvious that something is not quite right in here.

Quote:

Originally Posted by goodoleme

Technic,

The one HD-600/4 I came over with was NIB from JL. I did switch the amps (HD-600/4s) and I got the same uneven power output with the 2ohms vs 4ohms!

I did some thinking on this after Ken had pointed me to a post on DVC sub wiring: Even though the RIPS is maintaining constant wattage to the 2ohm channels, you still have 2x the voice coil which means you still have +3dB, assuming constant wattage.

Above 4ohms, the 600/4 will halve the available power...i.e. 75wpc. But since you still have 2x voice coil you get that 3dB back, so you are back to (rears+sides)=fronts. Thus I think you should wire in series (according to the manual this is a supported load).

Edit: I can't account for the different behavior of the PDX under this theory.

Hmmm, interesting. I've got the OEM sides/rears in parallel (1 ohm) running off one channel pair on the HD900/5. The fronts (4 ohm) are driven by the HD600/4. With gains set to minimum on "low" (2V) the rears are a few dB louder than the front doors. Theoretically, the max output of the HD900/5 at 1 ohm is 75W and that of the HD600/4 at 4 ohm 150W, so the fronts should be a lot louder, but they are not. I'm not worried about it though since I can raise the gains on the front channels to compensate.

The "low/High" input switch discussion though has got me thinking. I've had a problem with noise on the HD900/5 amp. When I switch from low to high, the noise goes away but of course the output level gets reduced and of I raise the gain to compensate, the noise comes right back. I was thinking, since the MS-8's speaker level outputs are of very good quality, what if I used those instead of the low level RCAs? Any potential downsides to doing that? This may be a good solution since it would kill 2 birds with one stone - getting rid of the engine noise AND utilizing the reportedly superior input option on the HD amps.

My HD600/4 has the same issues as reported above, but I've determined its an input signal issue (present even with the OE HiFi amp). The car is an E82 with HiFi + Technic harness adapter. Taking the front channels from the harness to the HD in conjunction with the low input setting (gains at min), I get noise. Switching to high voltage removes the noise but as mentioned above, it returns when the gains of the amp are turned up.

Recently I ran the front channels from the Technic harness into a Mosconi 6to8 DSP. This processor has low/high input settings as well. Interestingly, I ended up using a high voltage input configuration to the 6to8 and retained the low voltage setting at the input of the HD. Other combinations resulted in what sounded like a really compressed signal; very poor sound quality with an unnatural dynamic range.